Divide the following complex numbers: $\dfrac{9 e^{\pi i / 4}}{ e^{7\pi i / 4}}$ (The dividend is plotted in blue and the divisor in plotted in green. Your current answer will be plotted orange.)
Solution: Dividing complex numbers in polar forms can be done by dividing the radii and subtracting the angles. The first number ( $9 e^{\pi i / 4}$ ) has angle $\frac{1}{4}\pi$ and radius 9. The second number ( $ e^{7\pi i / 4}$ ) has angle $\frac{7}{4}\pi$ and radius 1. The radius of the result will be $\frac{9}{1}$ , which is 9. The difference of the angles is $\frac{1}{4}\pi - \frac{7}{4}\pi = -\frac{3}{2}\pi$ The angle $-\frac{3}{2}\pi$ is negative. A complex number goes a full circle if its angle is increased by $2 \pi$ , so it goes back to itself. Because of that, angles of complex numbers are convenient to keep between $0$ and $2 \pi$ $-\frac{3}{2}\pi + 2 \pi = \frac{1}{2}\pi$ The radius of the result is $9$ and the angle of the result is $\frac{1}{2}\pi$.